I bought the Holmes edition of D&D some years ago, and I've got to say that I'm really impressed with it! It was only supposed to be an introduction to gear up towards AD&D but I've often wondered what would've happened if Holmes had edited some supplemental material for it.

Well, it seems a few Holmes fans have done just that!

First there's Meepo's Holmes Companion. It's only four pages long, but it takes your characters up to level 9!

Then there's Holmes Blue Book Companion by R.C. "Thorkhammer" Pinnell. It's about 12 pages and takes characters to level 14 and also adds the character classes of Barbarian, Ranger, and Paladin.